1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of handling Short Message Service (SMS) acknowledgement messages between cooperating Mobile Switching Centers (MSCs) during a voice call involving handoff in a radio telecommunications network.
2. Description of Related Art
A Mobile Station-based Short Message Entity (MS-SME) is a mobile station that is capable of sending, receiving, and processing SMS messages. When a MS-SME originates a SMS message on a Digital Traffic Channel (DTC) while the MS-SME is in the service area of a first MSC, and the MS-SME then moves into the service area of a second MSC, the MS-SME cannot receive an acknowledgement of the SMS message. Existing telecommunication standards support only a static situation in which a MS-SME remains in the service area of one MSC from the time that the SMS origination is made until the MS-SME receives the SMS acknowledgement. The MSC can be either an anchor MSC where a voice trunk is first established for the MS-SME, or it can be a serving MSC where the MS-SME is currently operating. If the MS-SME makes a SMS origination on a DTC in an anchor MSC, the anchor MSC delivers the SMS message directly to a Message Center (MC). The anchor MSC then receives a SMS acknowledgement from the MC which is then delivered to the MS-SME.
If the MS-SME makes a SMS origination on a DTC in a serving MSC, the MS-SME must remain in the serving MSC until the SMS acknowledgement is received. The serving MSC forwards the SMS message to the anchor MSC. The anchor MSC delivers the SMS message to the MC and receives a SMS acknowledgement from the MC. The anchor MSC returns the acknowledgement to the serving MSC which, in turn, sends the SMS acknowledgement to the MS-SME.
However, during the time between the SMS origination on the DTC in the serving MSC, and receipt of the SMS acknowledgement at the MS-SME, the MS-SME may move from the serving MSC to another MSC. There is currently no method for delivering the acknowledgement to the MS-SME if the MS-SME changes MSCs during this time period. If the MS-SME does not receive an acknowledgement within a predetermined time period of its SMS origination (for example, 12.8 seconds in IS-136), the MS-SME may re-initiate another SMS origination message on the DTC. This unnecessarily utilizes network resources since it requires at least one additional ANSI-41 message between the anchor MSC and the new serving MSC, two ANSI-41 messages between the MS-SME's anchor MSC and the MC, and one IS-136 message between the MS-SME and the new serving MSC. Processing capacity is also needlessly utilized to process the repeated SMS message. Considerable bandwidth may be utilized since an SMS message may be up to 255 octets in length.
There are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein. In order to overcome the disadvantages of existing solutions, it would be advantageous to have a method of handling SMS acknowledgement messages that enables a MS-SME to receive an acknowledgement even if the MS-SME moves from one MSC to another after the SMS origination and before the acknowledgement is delivered. The present invention provides such a method.